1. Field
One embodiment of the invention relates to an image expansion apparatus that expands an image by pixel interpolation and a method thereof.
2. Description of the Related Art
An image expansion apparatus is used in, for example, a digital television apparatus, to enlarge a digital image. Such an image expansion apparatus creates a new pixel line between already existing pixel lines, thereby enlarging a digital image. Upon creating the new pixel line, the image expansion apparatus calculates a pixel value of a pixel to be interpolated based on pixel values of already existing pixels.
As an example of such an image expansion apparatus, Japanese Patent Application Publication (KOKAI) No. 2007-60104 discloses an interpolation pixel generating apparatus that generates an interpolation pixel to be interpolated at a position based on an input image containing a plurality of input pixels. More specifically, the interpolation pixel generating apparatus calculates, based on the input image, an autocorrelation value in a range including the position with respect to each of a plurality of directions from the position. The interpolation pixel generating apparatus then detects a direction with a maximum autocorrelation value, and, based on the input image, generates the interpolation pixel using an interpolation filter corresponding to the direction with the maximum autocorrelation value.
When the pixel value of a newly generated pixel is obtained based on the pixel values of pixels located in a diagonal direction with respect to the new pixel, the pixel value may be erroneously interpolated. Especially, when an edge extends at an angle in an image and the angle is large, the edge may be jagged (so-called “jaggies” may occur along the edge).